Coasts Flashcards
define fetch
distance over uninterrupted water that wind blows to generate waves
define littoral zone
area of shoreline from the sea to the land which is subjected to wave action. divided into 4 subzones: offshore, nearshore, foreshore and backshore
define spring tide
higher tide than normal due to sun and moon alignment, increasing grav pull. occur twice a month
define neap tide
lower tide than normal due to sun and moon being perpendicular, decreasing grav pull. occur twice a month
define geological structure and give examples
the way the rocks are arranged eg. joints, faults, dip, folds
define lithology
physical characteristics of each individual rock type
define morphology and give example
shape of coastal landscape eg. Haff coastline, dalmation coastline
define sub-aerial process and give examples
processes that occur at the base of the atmosphere (on land) eg. weathering, mass movement
what is a halophyte
salt-tolerant plant species
what is a storm surge
unusually high tide caused by strong winds pushing water towards shore, creating large waves. can also be caused by low pressure systems pulling water upwards and creating large waves.
what is the offshore
-1st stage of littoral zone
-fully submerged area of deeper water before the point at which waves begin to break.
what is the nearshore
- 2nd stage of littoral zone
- area of shallow water where friction between seabed and waves distorts the wave enough for it to break.
what is the foreshore
-3rd stage of littoral zone
-area between high and low tide mark
what is the backshore
-4th stage of littoral zone
-area above high tide mark, affected by wave action only during major storm events.
3 coastal types
- rocky, cliffed coastline - high relief, areas of resistant geology, high energy environments where erosion is greater than deposition, high no of destructive waves.
- sandy coastline - low relief, less resistant geology, low energy environments where deposition is greater than erosion, high no of constructive waves, sand dunes and beaches
3.estuarine coastline - low relief, saltmarshes and mudflats, low energy environment where deposition is greater than erosion, at mouth of river, less resistant geology
what is wave refraction
-Waves breaking early as they reach shallow water around an extending headland, which causes them to bend around the headland. This means that energy concentrates at the headland and maximum erosion occurs here. The bay is sheltered as wave energy has been lost, meaning deposition can occur.
define sediment cell
stretches of shoreline where the movement of material interacts in a closed system w little to no input or output of sediment
what is a sediment budget
total amount of sediment within a sediment cell
features of sediment cells
-usually bordered by headlands
-consists of sources (zones of erosion), sinks (zones of deposition) and transportation processes.
-amounts of erosion and deposition are balanced within cell (dynamic equilibrium)
-can be disturbed by human activity or natural changes eg. climate change
what is a dalmation coastline
- example of concordant coastline
-series of islands that run parallel to each other left exposed after sea levels rise and fill in river valley, leaving only ridges exposed
-eg. Croatian coastline
what is a haff coastline
-example of concordant coastline
-low-energy, unconsolidated environments behind bars that form lagoons w deposition of mud and sands
-eg. polish coastline on baltic sea
what is a concordant coastline
bands of rock run parallel to coastline - form straighter coastlines as sea can only break through in areas of weakness.
what is a discordant coastline
bands of rock run perpendicular to the coastline, forming headlands and bays that can be affected by wave refraction.
igneous rock - formation, examples, erosion rate and permeability
-lava cooling after reaching the surface. often have cooling joints, however usually have fewer weaknesses than other rock types
-granite, basalt
-Very slow erosion - less than 0.1cm/yr due to strong interlocking crystals
-impermeable
metamorphic rock - formation, examples, erosion rate and permeability
-formed from other rocks changing chemical composition under extreme heat and pressure at they are buried deep
-marble
-slow erosion rate - 0.1-0.3cm/yr - no joints or bedding plates but often folded and heavily faulted which marine processes can exploit
-impermeable
sedimentary rock - formation, example, erosion rate, permeability
-layers of sediment being deposited on top of each other and compressing until they eventually cement together due to minerals in sediment
- sandstone, limestone, chalk, clay
-moderate to fast erosion rate - 0.5-10cm/yr - often have weak bedding planes due to strata and often heavily jointed because of compaction and pressure release
-permeable
what is unconsolidated sediment/material
- sediment that has not been cemented to form solid rock (lithification)
- very easily eroded
-eg. Holderness coastline in Yorkshire retreates 2-10m/yr
what are joints
vertical cracks/fractures in cliff
what is strata
layers of rock
what are bedding planes
horizontal cracks in strata caused by gaps time time during periods of rock formation
what are folds
rocks crumpling inwards due to pressure during tectonic activity
cliff profile - horizontal, straight dip
-vertical profile
-easily eroded joints
cliff profile - dip towards sea (high angle)
-sloping, low-angled profile
-bedding planes - readily loosened by weathering
-landslides and block falls
- high recession rate
cliff profile - dip towards sea (low angle)
-steep profile w areas of overhanging rock
-block falls
-major cliff collapse when undercutting makes overhang unstable
-high recession rate
cliff profile - dip inland
-steep profile
-stable cliffs w low recession rate as grav forces pull loosened blocks into place.
micro-features of cliffs
-small scale features eg. caves, wave-cut notches
-form in areas weakened by heavy jointing or faults which have faster rates of erosion
examples of mechanical weathering
- freeze-thaw - when water gets into cracks between rocks and freezes. expansion puts pressure on rocks until they crack. forms talus scree slopes from shattered fragments of rock
2.salt crystallisation - when salt is deposited in cracks, accumulates and applies pressure. forms talus scree slopes
example of chemical weathering
-acidic rainwater - rainwater mixed w CO2 forms carbonic acids, which can dissolve carbonate rocks
examples of bio weathering
- burrowing animals/plant roots - widen cracks in cliffs and animals excavate material in partially weathered cliffs
2.boring molluscs - marine molluscs bore holes into cliffs by scraping surface which weakens rock
what is rotational slumping + what does it form
-type of mass movement
-when saturates soft rock/soils/unconsol material becomes too heavy and moves as a single mass along a slip plane. slow process
-forms rotational scar (fresh, unweathered, unvegetated surface) and terraced cliff profile
what are landslide + what do they form
-type of mass movement
-downslope movement of discrete blocks of rock down a flat slip plane, maintaining contact w surface.
-caused by mech weathering, marine erosion or rainstorms. occurs in consolidated rocks w joints/bedding planes sloping seawards
-forms talus scree slopes
what is a block fall + what do they form
-type of mass movement
-fragments of rock breaking away from the cliff face and falling vertically (not in contact w surface). very fast process
-often due to freeze-thaw, jointing/faults or marine erosion that undercuts cliff.
-forms talus scree slope
what is a mudflow
-type of mass movement
-occur when saturated soil and weak rocks flow down a slope
-typically occur when cliffs made of boulder clay eg Holderness
factors needed for deposition to occur
-small fetch
-sheltered area w little wind
-active erosion elsewhere
-shallow area
-low energy waves (constructive)
what is a drift-aligned coastline
-waves break at an angle to shoreline consistently, meaning there is constant LSD
what is a swash aligned coastline
-waves break parallel to shoreline, so little LSD
-forms cusps
differences between sandy beaches and shingle beaches
sandy:
-gentle sloping profile
-becomes compacted when wet w little percolation
-most swash returns as backwash as material is carried back down beach (through ridges)
shingle:
-steeper profile
-water percolates through shingle
-backwash limited
how do spits form + example
-long bank of sand extends out into the sea as LSD continues in straight line, even after change in coastline direction.
-changes in wind direction or sec winds can cause recurved spit (hooked end)
-eg. Spurn Point spit, Holderness
what is a bar + example
-landform of dep
-a spit that has been able to grow across a bay, connecting 2 headlands
-lagoons can form behind bar
-eg. Slapton bar, Devon
what is a tombolo + example
-landform of dep
-a spit joining an island to a mainland
-eg. Chesil beach joined to isle of portland
what is a cuspate foreland + example
-landform of dep
-triangular shaped headland
-occurs when LSD in opposing directions meets at boundary of 2 sediment cells
-eg. Dungeness, Kent
what is a storm beach
-landform of dep
-strong swash at high tides during spring tide storms will have enough energy to carry and deposit bigger boulders to the back of beach
-build up a ridge as following tides cannot reach material
what is a cusp
-landform of dep
-crescent-shaped indentations that form at swash-aligned beaches
-once curve indent is created, backwash removes more material
what is a berm + example
-landform of dep
-series of ridges formed after a storm beach that mark the successive high tides that follow the spring tide (get closer to the sea)
-eg. Hornsea beach, Holderness
6 stages of sand dune succession (brief)
- embryo dunes
- fore dunes
- yellow dunes
- grey dunes
- dune slack
- mature dune (climatic climax community)
what are embryo dunes
-1st stage, closest to sea, youngest
-sand blown by wind has been trapped by obstacles eg. plant, driftwood, litter and forms a small mound
-pioneer plants colonise freshly deposited sediment, stabilising it, add organic matter that retains moisture, reduce evaporation in sand
-plants that colonise are halophytes (salt-tolerant) eg. Saltwort
what are foredunes
-2nd stage behind embryo dunes
-increase in halophytes eg. Couch grass, Lyme grass that stabilise dunes
what are yellow dunes
-3rd stage, sit above beach level
-diversity of organisms and plants increases eg. Marram grass
-dead organic matter mixed into sand, making it more nutrient-rich allowing more plants to grow
what are grey dunes
-4th stage, fixed dunes - more protected from wind and stabilised by vegetation
-lots of vegetation (not salt-tolerant)
-organic matter mixed w sand, giving it darker colour
what is a dune slack
-dip between sand dunes - may be moist or filled w water
-nutrient rich and home to variety of plants/animals
what is a mature dune
-6th stage, oldest
-climatic climax community - woodland area w non-salt-tolerant plants eg. pine/birch trees, brambles
-far above high tide level
requirements for sand dune formation
-plentiful supply of sand - active erosion elsewhere
-strong winds to transport sand inland
-obstacles to trap sand eg. plants, shells, driftwood, litter
what is eustatic sea level change
global scale sea level change resulting from a change in volume of water in ocean
what is isostatic sea level change
local scale sea level change (relative to level of land), resulting from an isostatic adjustment (land moving up or down)
landforms of submergence
- ria - submerged RIVER valley
-section of river valley flooded by the sea, making it wider
-have steep-sided V-shaped valleys
-eg. South Devon coast - fjord - submerged GLACIAL valley
-glaciers carved out valley during ice age that have since melted
-leave behind steep-sided U-shaped valleys
-can be 1000s of metres deep
-eg. Sognefjord in Norway
landforms of emergence
- raised beaches
- beaches or wave-cut platforms above current sea level - relic coastline/fossil beach
- cliffs containing wave-cut notches/caves/arches above current sea level
-provide evidence of formation by marine erosion
impacts of sea level change - Kiribati
-islands - most only 0.5m above current sea level
-rising sea levels could cause ground water contamination, affecting ability to grow crops, threat of islands being submerged in next 50 yrs, ppl become environmental refugees
-have ‘migration w dignity’ policy - ppl temporarily migrate to Aus/NZ to gain skills for when theyre forced to leave so they will not be dependent on state resources
-purchased land in Fiji for agriculture and fish farming to guarantee food security - could also be place ppl migrate to in future
-planting mangrove forests to stabilise them and provide protection against storms and reduce coastal flooding
local factors increasing flood risk in Bangladesh
- land subsidence - due to embankments built to protect crops stopping natural deposition that maintains height of island.
- removing mangrove forests - 71% of mangroves retreating due to sea level rise, erosion and deforestation.
- deforestation in himalayas - less interception = more surface run off into rivers = delta area where main rivers converge has higher flood risk
- monsoon climate - more cyclones and storm surge events. lack of development of coastal defences exacerbate this issue
1953 storm surge - HICs
-UK and Netherlands
-caused by exceptionally high spring tide, low pressure system and funnelling shape and shallowness of North Sea
-depression in pressure caused sea level to rise, causing significant flooding
-1800 killed in Netherlands, 300 in England
-lack of warning systems (radio only) and emergency planning caused high death toll
2007 storm surge - Bangladesh
-6m storm surge due to category 4 cyclone, funnel shape of Bay of Bengal and deforestation of mangrove swamps
-15,000 killed and 1.6 million homes destroyed
-$1.7 billion damage
2013 storm surge - UK
-storm coincided w spring tide and caused storm surge
-improved emergency warning systems and evacuation plans meant NO deaths
-1400 homes damaged
4 strategies of coastal management
- hold the line - maintain current position
- advance the line - extending high tide line out towards sea and building wider beach
- managed retreat/realignment
- do nothing - no active intervention - allowing nature to take its course
hard engineering strategies
- groynes
- sea wall (straight or recurved)
- rip rap
- revetments
- offshore breakwaters
- gabions
what are revetments
-wooden fences built before cliffs to break waves early and dissipate wave energy to prevent cliff retreat
what are gabions
-mesh cages filled w rocks often at base of cliffs
-encourage infiltration/percolation and reduce cliff retreat
soft engineering strategies
- beach nourishment
- cliff regrading and drainage
- dune stabilisation
- managed retreat/realignment
reasons for holderness coastal erosion
-unconsolidated, low resistant material (boulder clay)
-lack of sea defences in most places
-sub-aerial processes (weathering causing mass movement)
-intense low pressure systems causing storms
-relatively deep sea floor before cliffs
what is terminal groyne syndrome + example of location
-higher rates of erosion immediately south of sea defences (particularly groynes) as they starve beaches further down coast of sediment due to interruption of LSD
-eg. Mappleton on Holderness coast
reasons for coastal management in Netherlands
-50% 1m or less above sea level
-extremely large coastline due to islands and peninsulas
-major flooding problems eg. 1953 storm surge that killed 1800 ppl
Netherlands coastal management
- zuider zee -
- 30km barrier to cut off land from sea
-created reclaimed land (used for urban expansion and agriculture) and freshwater lake behind - delta works -
- series of dams to reduce size of coastline
-have channels for ports
-storm surge barriers that can be closed when needed (when sea rises above 3m) - dune stabilisation -
- planting vegetation
-groynes
-beach nourishment
-areas fenced off to prevent trampling
Lyme Regis coastal management
4 stages:
1: short sea wall and promenade built
2: stone groynes, rip rap, beach nourishment, drainage improvements in cliffs
3: cancelled due to CBA
4: 390m sea wall, 19m nails pinned into cliff to prevent mass movement
-around £60million spent in total
-only last around 50yrs
-increased tourism - larger beaches, new promenades, easier access
Medmerry coastal management
-managed realigment
-110m breach in existing sea defences to create intertidal zone, saltmarsh and nature reserve (180 acres)
-embankments built 2km inland - much less expensive to maintain as intertidal zone absorbs wave energy
-new wildlife habitats created and attracted green tourism
-300 homes, caravan park, sewage works and main road protected
-£28 million to construct
-3 farms lost
